docs: def writeKerning(self, location=None, masters=None):
          """ Write kerning into the current instance.
              Note: the masters attribute is ignored at the moment.
          """
          if self.currentInstance is None:
              return
          kerningElement = ET.Element("kerning")
          if location is not None:
              locationElement = self._makeLocationElement(location)
              kerningElement.append(locationElement)
          self.currentInstance.append(kerningElement)